1. Field of the Invention
The present invention relates to a polymerizable composition that can be used in image forming materials such as three-dimensional rapid prototyping, holography, planographic printing plate precursors, colorproofs, photoresists, and color filters, as well as photocurable resin materials such as inks, paints, and adhesives.
In particular, the invention relates to a polymerizable composition that is suitable for use in negative-working planographic printing plate precursors, which can be directly made by using various lasers from digital signals of computers and the like. The present invention also relates to a negative-working planographic printing plate precursor using the composition.
2. Description of the Related Art
In recent years, solid lasers, semiconductor lasers, and gas lasers, which radiate ultraviolet rays, visible rays or infrared rays having wavelengths of 300 nm to 1,200 nm, have become more powerful, more compact, and easily available. These lasers are very useful as exposure sources during direct plate making from digital data of computers and the like.
There are various studies with respect to recording materials sensitive to these types of lasers. Representative examples of materials that can be recorded with infrared lasers having a photosensitive wavelength of 760 nm or more include the positive-working recording material described in U.S. Pat. No. 4,708,925 and the acid catalyst crosslinking type negative-working recording material described in Japanese Patent Application Laid-Open (JP-A) No. 8-276558. Further, many recording materials responsive to ultraviolet or visible lasers having wavelengths of 300 nm to 700 nm are known, and examples thereof include the negative-working recording materials utilizing radical polymerization described in U.S. Pat. No. 2,850,445 and Japanese Patent Application Publication (JP-B) No. 44-20189.
Negative-working image forming materials utilize a recording method in which a polymerization reaction occurs using radicals generated by light as an initiator, and exposed areas in the recording layer thereof are cured to form image areas. When compared with positive-working image forming materials in which solubilization of a recording layer occurs due to the energy from infrared laser irradiation, such negative-working image forming materials have low image forming properties. Therefore, in order to facilitate the curing reaction by polymerization and form firm image areas, heat treatment is generally carried out prior to development.
Image recording materials having photopolymerizable recording layers that use a photopolymerizable composition as a recording layer are known described in JP-A Nos. 8-108621 and 9-34110. Such recording layers excel at high-sensitivity image forming, however, when a hydrophilized substrate is used as a support, adhesion at the interface between the recording layer and the support is low, thus printing endurance is poor when used as a printing plate. In contrast to the above, when a non-hydrophilized substrate is used, adhesion is enhanced, however, such a substrate is also problematic in that non-image portions are not completely removed and thus remain after development.
In negative-working planographic printing plate precursors, a polymer binder having an alkali-soluble acid group in a recording layer is used, and non-image portions are formed by developing with an alkaline developing solution and removing unexposed areas. As such alkali-soluble acid groups, carboxylic acid groups have been conventionally used. However, since carboxylic acid groups generally have low acid dissociation constants (pKa) (e.g., in the case of an acetic acid, the pKa is 4.74), they tend to dissociate due to penetration of alkaline developing solution. Accordingly, the developing solution tends to penetrate into cured image areas, whereby the interface between the support and the recording layer is damaged due to adhesion deterioration, which leads to deterioration in printing endurance.
In order to enhance adhesion between the recording layer and the support and prevent penetration of developing solution into the interface, a non-hydrophilized support may be used. In this case, however, staining tends to occur in non-image portions. In order to completely remove the non-image portions and prevent staining, it is necessary to use strong alkaline developing solutions having a pH of 13 or more. However, use of such strong alkaline developing solutions is problematic since these are liable to penetrate into and damage cured image areas, thereby deteriorating printing endurance.
Accordingly, as mentioned above, in conventional negative printing plate precursors, it is difficult to make both printing endurance and stain-resistance consistent with each other, and precursors having thoroughly satisfactory functions have yet to be obtained.